Sautéing is browning food first on one side and then on the other in a small quantity of fat or oil. When sautéing, which is a type of frying, the fat is placed in a shallow pan, and when it is sufficiently hot, the food is put into it. When cooking, the fat should not come up the sides of the food being cooked, the food basically cooking on a thin layer of fat. Foods that are to be sautéed are usually sliced thin or cut into small pieces, and they are turned frequently during the process of cooking. Sauté is French for "jumping", used to describe the action of the food in the pan as it is tossed around to prevent burning.
Foods prepared in this way can be difficult to digest, because they become more or less hard and can become soaked with fat if too much is used. Chops and thin cuts of meat, which are intended to be pan-broiled, are really sautéed if they are allowed to cook in the fat that renders out of them.
The term pan-frying is the English equivalent of sautéing (which is a French word). Some people consider it a different technique, which uses more fat and takes longer. Stir-frying uses higher temperatures and continual stirring.
Tips for Proper Technique
While different ingredients will call for variations in this technique, there are some general guidelines to help ensure an ideal outcome.
Mise en place
The first rule is be prepared. If your recipe calls for chopped ingredients in step 12, make sure you have them now. While experienced cooks will successfully chop the next ingredient while the rest are cooking, this is not a path to follow for the inexperienced. For one thing, chopping times for the experienced cook are generally much shorter, so the cooking food doesn't have a chance to burn. For another, the experienced cook can quickly assess whether food is done. A less experienced cook should be much more attentive to the pan to become more familiar with the stages of "doneness".
Heat the pan
Feel free to put a cold pan onto a cold burner before turning it on, but do not put cold oil into a cold pan and then try to heat. The reason is subtle: heat will eventually break down the chemical bonds of the oil and it will lose its lubricating properties. If that happens, your ingredients will stick to the hot surface and one side will blacken and burn, and the other side will remain raw or underdone.
The pan is hot enough if a few small drops of water flicked from your fingertips vaporise immediately, or if a larger drop of water hisses and floats across the surface of the pan on a cushion of its own steam. Do NOT add oil to the pan if there is hot water still there, as it may spatter vigorously. Clouds of oil droplets can be lit by open flame, and a fireball is never necessary for this particular cooking technique!
Heat the oil
Only after the dry pan is hot should you add enough oil to coat the bottom of the pan. The oil should begin to ripple, and spread quite quickly over the pan. If your pan was hot enough, this process should only take a few seconds. If your pan was too hot or if you wait too long, the oil will start to smoke, then turn brown, then burst into flame. Along the way you will have ruined a perfectly good pan, and possibly burned down your house.
Add the food
After your food item has been added, do not crowd the pan. If necessary, you should cook food in batches, removing each batch and reheating the pan and adding more oil as required. Also, unless the recipe specifically calls for it, do not cover the pan while cooking. Trapped steam from the cooking side of the food will soften the top side. Ideally sautéed item have a crispy outside, although this depends heavily on the food item (sautéed steak: crispy; sautéed carrots: not crispy)
Stir the food
Stir the food, don't shake the pan. Some cooks like the ostentatious technique of lifting the pan off the range and shaking it in the air, sometimes using the rounded edge of the sauté pan to flip the food over. Practice this to impress your uneducated friends (outside, with a cold pan, using dried split peas) but you should expect that the cooking time of your dish will be extended if you continually remove the pan from the heat source. Also, if the temperature drops too much, the oil will begin to soak into your food, and your dish will become greasy. If you feel the need to shake the pan, keep the pan close to your heating element if it is safe to do so.
The amount of attention required will depend on the recipe. For some recipes, constant stirring is required. Other times, especially when sautéing single cuts of meat, it is best to cook one side, then the other side, with no stirring or movement of the food item in the pan at all. In that case, plan to put the "skin" side or presentation side (the side facing up on the plate when served) down into the clean hot oil first.
Use the fond
When sautéing cuts of meat, many recipes will call for you to deglaze the pan with a flavorful liquid (e.g. stock, wine, spirits, or even fruit juices). The dark brown bits of meat left behind from the high heat cooking are called "fond" and are as intensely flavoured as pan drippings from roasted meats. These should generally be scraped off the bottom of the pan and dissolved into the deglazing liquid. In especially elegant preparations, the pan sauce created is strained to remove the solid bits, leaving only the dissolved flavourings in a smooth sauce.
When using garlic and onion
When sautéing with both onions and garlic, be sure to sauté the onions first until they are clear, then add the garlic, and continue to sauté until it is pale gold. The onion takes longer to cook, thus if both are added at the same time, the garlic will be browned by the time the onion is done, which results in an undesirable dominant pungency. Garlic will add its flavour much more harmoniously when only sautéed to a pale gold.